Hong Kong (AFP) -

Activists accused Beijing of crippling Hong Kong's parliament Friday after four pro-democracy lawmakers were disqualified.

More than 1,000 people protested near the government offices Friday night in response to the decision.

The High Court judgement came as a massive blow for the democracy movement as it means the balance of power in the partially elected legislature swings further to the pro-China camp because opponents do not have enough seats to veto bills.

Former Umbrella Movement protest leader Nathan Law was among those barred in a case brought by the semi-autonomous city's Beijing-friendly government after the four changed their oaths of office to reflect frustrations with Chinese authorities.

Law was one of several rebel lawmakers to secure a foothold in parliament at citywide elections in September.

But that triumph was soon jeopardised after Beijing issued a special interpretation of Hong Kong's mini-constitution in November to insist oaths be taken in a "sincere and solemn" manner.

The unprecedented intervention was prompted by a string of protests during the swearing in of lawmakers the month before.

The High Court said Friday Beijing's ruling was "binding" and the court's decision to bar the four retrospectively was not politically motivated.

Concerns China is squeezing Hong Kong have sparked calls by some activists for self-determination or even independence for the city, angering Beijing.

The dismissed legislators were not staunchly pro-independence but at least two of them have advocated self-determination for Hong Kong. 

Law's party Demosisto condemned "the manifest interference of the Beijing government to cripple Hong Kong's legislative power".

The 24-year-old was one of the most popular candidates to win a seat, gaining 50,000 votes. 

Human Rights Watch described the judgement as a "another alarming blow" to Hong Kong's autonomy.

Amnesty International said the decision confirmed the government wanted to "silence and effectively punish" criticism of the political system. 

At the rally Friday night, banned lawmaker Edward Yiu described it as "the darkest day in Hong Kong politics".

"The whole thing has gone insane," said protester Peggy Sui.

"I don't know how to describe how I feel besides anger."

Artist and activist Sampson Wong voiced pessimism at the rally. 

"Everyone in their speeches said although it feels hopeless, we need to persist... but they can't seem to say how it's possible to stop these things from happening again," said Wong.

- Xi's 'red line' -

The court judgement comes two weeks after Chinese President Xi Jinping warned any challenge to Beijing's control over Hong Kong crossed a "red line" when he visited the city to mark 20 years since it was handed back to China by Britain.

The handover agreement enshrined liberties unseen on the mainland, including freedom of speech and an independent judiciary, but Beijing has been accused of trampling the deal.

Two pro-independence legislators have already been disqualified by the High Court over their oaths.

The cases against them and the other four lawmakers were initiated under the previous Hong Kong administration, led by unpopular former chief executive Leung Chun-ying.

He was succeeded by Carrie Lam on July 1, who is also seen as a puppet of Beijing by critics.

The oath requires lawmakers to repeatedly describe Hong Kong as a Special Administrative Region of China. 

Law quoted Gandhi before taking his pledge, saying: "You will never imprison my mind", and used intonation to make his oath sound like a question.

The judgement said Law "was objectively expressing a doubt on or disrespect of the status of the People's Republic of China as Hong Kong's legitimate sovereign country".

Veteran activist Leung Kwok-hung raised a yellow umbrella -- a symbol of the democracy movement -- which the court said did not reflect the "importance and seriousness" of the ceremony.

Former protest leader Lau Siu-lai failed to convey the oath's proper meaning by reading her pledge at a snail's pace, the court ruled.

Edward Yiu added lines to his oath, saying he would "fight for general universal suffrage", which rendered his pledge invalid according to the judgement.